Indeed, the Palace manager has made just four changes from his last Premier League clash: Jack Butland replaces Vicente Guaita in goal and Tyrick Mitchell, James McArthur and Christian Benteke are replaced by James Tomkins, Jordan Ayew and Jean-Philippe Mateta.
Joel Ward will captain the Eagles in their first League Cup outing of 21/22, with Palace hoping to repeat their pre-season success over Watford in the 19:45 BST kick-off.
Gallagher, who starts in midfield, will be looking to build on his successful competitive debut against Brentford last Saturday; a game in which the recent signing earned Man of the Match.
Watford have made a host of changes since losing 2-0 to Brighton & Hove Albion, with players such as Ben Foster, Danny Rose and Josh King making the lineup.
Watford: Foster, Rose, Sieralta, Ekong, Ngakia, Etebo, Louza, Sema, Fletcher, Hernandez, King.
Subs: Elliott, Cleverley, Cathcart, Femenia, Dennis, Baah, Alvarado.
Palace: Butland, Tomkins, Andersen, Guéhi, Ward, Schlupp, Kouyaté, Gallagher, Ayew, Zaha, Mateta.
Subs: Guaita, Mitchell, Kelly, Riedewald, McArthur, Rak-Sakyi, Benteke.